Method of adhering urethane foams

ABSTRACT

A method of adhering rigid urethane foam to itself and to various substrates, such as paper and metal, by means of carefully controlling heat and pressure. The polyurethane foams capable of adhesion are those which allow a post cure at elevated temperature subsequent to their original formation.

United States Patent Rush 1451 Dec. 19, 1972 54] METHOD OF ADHERING URETHANE 3,205,120 9/1965 Flanders ..l56/306 FOAMS 3,362,862 1/1968 King ..156/306 [72] Inventor: Donald J. Rush, Grandview MO 3,547,753 12/1970 Sutton 156/306 [73] Assignee: Butler Manufacturing Company, FOREIGN PATENTS OR APPLICATIONS Kansas City, 824,668 12/1959 Great Britain ..156/30 [22] Filed: Jan. 22, 1970 OTHER PUBLICATIONS [52] US. Cl. ..l56/306,156/78,156/331, 161/160, 161/190 [51] Int. Cl. ..C09j 7/00 [58] Field of Search ..156/306, 78, 79; 161/190 [56] References Cited UNITED STATES PATENTS 2,994,110 8/1961 Hardy ..161/190X 3,463,698 8/1969 Yanagihara et a1... ....16l/190 X 3,563,845 2/1971 Stevens ....161/190 X 3,497,416 2/1970 Critchfield et a1 ..l56/306 2,957,793 10/1960 Dickey ..156/306 3,062,698 11/1962 Aykanian ..156/306 Materials Handbook by G. S. Brady, 9th Edition Mc- Primary Examiner-Reuben Epstein Attorney-Shoemaker & Mattare [57] ABSTRACT A method of adhering rigid urethane foam to itself and to various substrates, such as paper and metal, by means of carefully controlling heat and pressure. The polyurethane foams capable of adhesion are those which allow a post cure at elevated temperature subsequent to their original formation.

3 Claims, No Drawings METHOD OF URETHANE FOAMS BACKGROUND OF THE INVENTION use of adhesives have required subsequent steps to thefoaming process along with the necessity of special apparatus. Even with the use of adhesives, these processes have resulted in interface imperfections, such as voids,

and also residual thermoplasticity after the foam has cooled.

There would be, therefore, advantages for a new method of adhering thermosetting polyurethanefoams to selected materials and for joining polyurethane foams to themselves. This is particularly true when the foams are used in structural and insulating capacity, such as in sandwich panels, in view of the fact that there would be 'no necessity for using other adhering materials. There is also no necessity for obtaining particular adhesives which would be compatible with the foam and with the materials to which it would be adhered.

SUMMARY OF THE INVENTION It is accordingly one object of the present invention to provide a new process for adhering urethane foam to itself and to selected materials wherein no adhesive is necessary.

Another object of the invention is to set forth a new process wherein temperature and pressure are carefully controlled so as to adhere a certain class of polyurethane foams to materials and to itself without the necessity of an adhesive.

Yet another object of the invention resides in the production of foam sandwiches wherein there is improved adhesion to the foam and no residual plasticity after cooling.

A further object of the invention resides in the method for improving the adhesion of selected materials to thermosetting polyurethane foams having improved surface or interfacial characteristics of the composite.

These and other advantages of the present invention will become apparent from the following description and examples. I I

In accordance with the above objects, it has been found that certain thermosetting polyurethane foams which are susceptible to post curing after foaming can I be adhered to themselves and to other selected materials by carefully controlling the pressure and the temperature to which they are subjected.

The polyurethane foams which are capable of post curing are those foams produced by reacting a polyisocyanate with a methylol resin having reactive methylol groups, a pH preferably higher than 3.0 and a water content not in excess of about percent. While the phenolic methylol resins are preferred, similar results can be obtained starting with methylol resins based upon compounds such as urea, melamine, aniline and paratoluene sulfonamide. With regard to the polyisocyanate, any polyisocyanates ordinarily used in polyurethane foam production can be used with these resins. The component parts are present in a ratio of one-half to 1% parts by weight of polyisocyanate to 1 part by weight of methylol resin.

To improve the physical properties ofthe above formed foamed resins, they are usually cured at a temperature of from 250-500F., or for periods of time averaging aboutone-half to 1 hour.

It has been found that by applying heat (e.g., 350-400F.) and very low pressures for less than a minute to a rigid or a flexible adherent material, such as paper, metal, coated paper, or to foam, while such is in contact with a methylol polyurethane foam which has not yet been post cured, an improved degree of adhesion of skin to cellular plastic or cellular plastic to cellular plastic can be obtained. The heat and pressure soften and partially tackify the cellular plastic, which is compressed and densified near its heated surface causing a smoothing or flattening of the treated surface.

This process has the advantage of improved adhesion of selected skins to a cellular plastic thermosetting polyurethane foam). No adhesives or adhesion promoters are required and adhesion is obtained in a very short time. There is a reduction of slight interface imperfections, such as voids, when pressure is applied to the softened cellular plastic. There is no liquid stage and post sizing of panels to thickness while improving adhesion is I effected without any residualv thermoplasticity after the foam has cooled.

Description of the Preferred Embodiments foam undermoderate pressure andtemperatures of from 350-400F. can be adhered to themselves or to other substrates, such as metal, paper or coated paper.

The following specific examples will more clearly define and illustrate the invention:

EXAMPLE I A foamed-in-place, paper-skinned panel was made consisting of two'paper (kraft liner board) skins. On one a foamable phenolic-isocyanate mix was poured which expanded, rose and contacted the top skin. The panel was cooled to room temperature. It was placed between it inch thick aluminum plates, which had been preheated to about 350F., for about 1 minute. The weight of the top plate supplied about 0.1 psi to the panel. The bond was paper-tearing as demonstrated by a peel test. Additional benefits were apparent in that the panel surfaces (skins) were smoothed, removing waves or wrinkles, and the foam interface was densified, which provided a stronger and more damage resistant panel surface. An identical panel which was not treated by the above method offered little or no paperto-foam bond, contained slight waves on its surface and had a softer surface.

EXAMPLE.

Two rectangular pieces of the plastic foam described above, with'saw-cut surfaces about 1% inches thick, were placed in an end-to-end contact relationship. A is inch thick strip of the same foam was placed on both sides of the narrow gap defining the end-to-end joint, the strips completely covering and overlapping the joint. The foam assembly was placed between aluminum plates, which were preheated to about 400F.

EXAMPLE Ill paper adhered to the foam surface and the foam was compressed and densified near its surface.

Having thus described the process of the instant invention in terms of its specific embodiments which are set forth in the description and the examples of the aforesaid specification, it is apparent to those skilled in the art that various changes and modifications can be made in the process without departing from the spirit and scope of the invention.

1 claim:

1. A process of bonding rigid, thermosetting polyurethane foam to itself and to other substrates, said polyurethane foam being capable of being postcured and formed by reacting a methylol resin with a polyisocyanate in a ratio of one-half to 1% parts by weigh of polyisocyanate to 1 part by weight of methylol resin, the methylol resin having reactive methylol groups, a

- pH of at least 3 and a water content of less than 10 per- A piece of kraft liner board (26 pound), which had i cent, comprising placing the foam next to the substrate to which it is to be bonded and applying heat of a temperature of about 350 to 400 F. and moderate pressure.

2. The process of claim 1 wherein the pressure applied is O.l psi.

3. The process of claim 1 wherein the substrates are selected from the group consisting of polyurethane foam, paper, metal and coated paper. 

2. The process of claim 1 wherein the pressure applied is 0.1 psi.
 3. The process of claim 1 wherein the substrates are selected from the group consisting of polyurethane foam, paper, metal and coated paper. 